otelzap: Use pool for encoder

[khushijain21]

Part of https://github.com/open-telemetry/opentelemetry-go-contrib/issues/5191

Pre-work https://github.com/open-telemetry/opentelemetry-go-contrib/pull/5279

Results:

goos: linux
goarch: amd64
pkg: go.opentelemetry.io/contrib/bridges/otelzap
cpu: 12th Gen Intel(R) Core(TM) i5-1245U
                           │ old_bench.txt │            new_bench.txt             │
                           │    sec/op     │    sec/op     vs base                │
CoreWrite/10_fields-12        872.7n ± 73%   473.1n ± 52%  -45.78% (p=0.000 n=10)
CoreWrite/20_fields-12        2.033µ ± 13%   1.660µ ±  6%  -18.35% (p=0.000 n=10)
CoreWrite/Namespace-12        1.647µ ± 31%   1.033µ ±  3%  -37.28% (p=0.000 n=10)
CoreWrite/With10_fields-12    219.9n ± 19%   218.8n ±  7%        ~ (p=0.912 n=10)
CoreWrite/With20_fields-12    468.6n ± 21%   497.0n ± 23%        ~ (p=0.393 n=10)
CoreWrite/WithNamespace-12    14.64n ± 13%   17.23n ± 21%  +17.69% (p=0.014 n=10)
geomean                       404.9n         339.1n        -16.26%

                           │ old_bench.txt │            new_bench.txt             │
                           │     B/op      │    B/op     vs base                  │
CoreWrite/10_fields-12        978.0 ± 0%     307.0 ± 0%  -68.61% (p=0.000 n=10)
CoreWrite/20_fields-12       2180.0 ± 0%     817.0 ± 0%  -62.52% (p=0.000 n=10)
CoreWrite/Namespace-12       1760.0 ± 0%     609.0 ± 0%  -65.40% (p=0.000 n=10)
CoreWrite/With10_fields-12    208.0 ± 0%     208.0 ± 0%        ~ (p=1.000 n=10) ¹
CoreWrite/With20_fields-12    640.0 ± 0%     640.0 ± 0%        ~ (p=1.000 n=10) ¹
CoreWrite/WithNamespace-12    0.000 ± 0%     0.000 ± 0%        ~ (p=1.000 n=10) ¹
geomean                                  ²               -41.35%                ²
¹ all samples are equal
² summaries must be >0 to compute geomean

                           │ old_bench.txt │            new_bench.txt             │
                           │   allocs/op   │ allocs/op   vs base                  │
CoreWrite/10_fields-12        13.00 ± 0%     10.00 ± 0%  -23.08% (p=0.000 n=10)
CoreWrite/20_fields-12        22.00 ± 0%     17.00 ± 0%  -22.73% (p=0.000 n=10)
CoreWrite/Namespace-12        16.00 ± 0%     12.00 ± 0%  -25.00% (p=0.000 n=10)
CoreWrite/With10_fields-12    1.000 ± 0%     1.000 ± 0%        ~ (p=1.000 n=10) ¹
CoreWrite/With20_fields-12    1.000 ± 0%     1.000 ± 0%        ~ (p=1.000 n=10) ¹
CoreWrite/WithNamespace-12    0.000 ± 0%     0.000 ± 0%        ~ (p=1.000 n=10) ¹
geomean                                  ²               -12.60%                ²
¹ all samples are equal
² summaries must be >0 to compute geomean

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 64.6%. Comparing base (ff65757) to head (8db2a5e). Report is 20 commits behind head on main.

Additional details and impacted files

[](https://app.codecov.io/gh/open-telemetry/opentelemetry-go-contrib/pull/5719?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-telemetry) ```diff @@ Coverage Diff @@ ## main #5719 +/- ## ======================================= + Coverage 64.5% 64.6% +0.1% ======================================= Files 200 200 Lines 12558 12585 +27 ======================================= + Hits 8101 8134 +33 + Misses 4220 4215 -5 + Partials 237 236 -1 ``` | [Files](https://app.codecov.io/gh/open-telemetry/opentelemetry-go-contrib/pull/5719?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-telemetry) | Coverage Δ | | |---|---|---| | [bridges/otelzap/core.go](https://app.codecov.io/gh/open-telemetry/opentelemetry-go-contrib/pull/5719?src=pr&el=tree&filepath=bridges%2Fotelzap%2Fcore.go&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-telemetry#diff-YnJpZGdlcy9vdGVsemFwL2NvcmUuZ28=) | `90.0% <100.0%> (+<0.1%)` | :arrow_up: | | [bridges/otelzap/encoder.go](https://app.codecov.io/gh/open-telemetry/opentelemetry-go-contrib/pull/5719?src=pr&el=tree&filepath=bridges%2Fotelzap%2Fencoder.go&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-telemetry#diff-YnJpZGdlcy9vdGVsemFwL2VuY29kZXIuZ28=) | `87.3% <100.0%> (+1.4%)` | :arrow_up: | ... and [13 files with indirect coverage changes](https://app.codecov.io/gh/open-telemetry/opentelemetry-go-contrib/pull/5719/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-telemetry)

[pellared]

Please make sure to add benchmarks to the PRs which are meant to improve performance. You can also consider creating separate PRs that would contain just benchmarks.

[pellared]

Please use https://pkg.go.dev/golang.org/x/perf/cmd/benchstat to show the performance improvement (between main and this branch) in the PR description.